The information provided herein is provided solely to assist the understanding of the reader, and do not constitute an admission that any of the information is prior art to the present invention.
There is a need for hydrocarbon energy sources as feedstocks and in consumer products and a growing concern over the depletion of the presently available hydrocarbon resources and declining quality of the hydrocarbons produced. There is therefore a need for the recovery of hydrocarbons from other sources in an efficient and cost-effective manner. One suitable source of hydrocarbons is oil shale found in subterranean sedimentary formations.
Oil shale is commonly defined as a fine-grained sedimentary rock containing organic matter (kerogen) that yields substantial amounts of oil and combustible gas upon destructive distillation or exposure to heat. Kerogen is a solid, insoluble hydrocarbon that has been converted by natural degradation (e.g., by diagenesis) and that principally contains carbon, hydrogen, nitrogen, oxygen, and sulfur. Most of the organic matter is insoluble in ordinary organic solvents and it must be decomposed by heating to release such materials.
Oil shale deposits are found throughout the world. They range in age from Cambrian to Tertiary and were formed in a variety of marine, continental and lacustrine-depositional environments. For example large areas of north-western Colorado, north-eastern Utah and south-western Wyoming are known to contain very large deposits of oil rich shale. Much of this oil rich shale is situated in the Mahogany Zone at a depth of approximately 1475 ft (450 m) and is estimated to contain 213 billion tons of in-situ shale oil. Within Colorado is the Piceance Basin. This basin contains an upper bedrock stratigraphy of basin-fill sediments from the tertiary period containing sandstone, siltstone and maristone. Below it is the Green River Formation which may be up to 5000 ft (1525 m) thick. It contains keragenous dolomitic maristone and shale, sandstone, claystone, siltstone and clay-rich oil shale. The grade of oil shale varies with location and depth. In some areas, substantial quantities of saline minerals such as nahcolite, dawsonite and halite are intermixed or intermingled with the oil shale. Nahcolite (sodium bicarbonate —NaHCO3) generally occurs at proportions less than 5 wt % however in lower oil shale zones it may average more than 30 wt %. Dawsonite (dihydroxy sodium aluminium carbonate —NaAl(OH)2CO3) and other saline minerals may be present in amounts up to 15 wt % (3 to 5 wt % on average).
Because of the depth of the oil shale and the thermal decomposition of nahcolite and dawsonite, it is generally considered that it would not be viable to conventionally mine and process the oil shale in an economical or environmentally friendly manner above ground.
It would be desirable to find a method for in-situ processing of oil shales.